A high-pressure feedthrough is often used within a hydraulic or pneumatic system in which a signal transmission should take place between regions having high pressure differences. A sufficient sealing in the region of the cable feedthrough is important with possible pressure differences of several hundred bar.
Problems can arise on the feeding through of coaxial cables that are used for the signal transmission of high-frequency signals on the order of 10 GHz. An exemplary application for the required feeding through of coaxial cables between a low-pressure zone and a high-pressure zone is the LiView measurement process which uses a vector measurement of the scatter parameters of a hydraulic cylinder. The process works at measurement frequencies on the order of 10 GHz that have to be coupled into or decoupled from the cylinder, i.e. the signal cables have to be introduced into the cylinder region from the outside.
It is important for the signal quality and for the accuracy of the measurement process that the transmitted signals are not impaired by interference in the transmission path. Unwanted reflections due to impedance fluctuations of the coaxial cable can degrade signal quality and the measurement.
The object of the present disclosure is to provide a suitable high-pressure feedthrough for a coaxial cable that is able to satisfy the above conditions.
In accordance with the present disclosure the high-pressure feedthrough comprises at least one support structure that is provided with an elongate bore. The elongate bore extends through the support structure from a high-pressure side to a low-pressure side. The high-pressure side of the support structure is connected to the high-pressure zone of the system when fitted of the high-pressure feedthrough in a hydraulic or pneumatic system. Whereas, the low-pressure side of the support structure is connected to the corresponding low-pressure environment. The elongate bore consequently permits a connection between the two pressure zones.
The structural design of the elongate bore is selected such that at least the inner conductor of a coaxial cable can be laid continuously through the elongate bore from the low-pressure side to the high-pressure side.
Certain cable elements have to be removed at least in certain sections of the elongate bore for an ideal seal with respect to the high-pressure side. The inner conductor of a coaxial cable may extend without interruption through the elongate bore from the low-pressure side to the high-pressure side. In sections of the elongate bore wherein parts of the coaxial cable have been removed, the functions of the removed parts are taken over by elements of the high-pressure feedthrough.
Possible connection points with impedance deviations are avoided by the interruption-free laying of at least the inner conductor of a coaxial cable through the total elongate bore, whereby the risk of signal reflections occurring can be reduced to a minimum. An interference-free transmission path with ideal electrical conducting properties can be provided when impedance jumps are consistently avoided. In addition, disclosed embodiments permits a compact construction shape and the integration of a plurality of functional elements produces cost benefits and reliability advantages.
In one embodiment, the transition of the outer conductor and/or of the dielectric of the coaxial cable to a component of the high-pressure feedthrough taking over the function of the outer conductor and/or dielectric takes place within the elongate bore. A small piece of the coaxial cable may accordingly project from the low-pressure side into the elongate bore. Removal of the protective jacket and, optionally, of the outer conductor and of the dielectric consequently only has to take place within the elongate bore. The transitions of the individual cable components to the components of the high-pressure feedthrough are particularly offset from one another in an axial direction. For example, the complete cable can, be inserted into the elongate bore from the low-pressure side. After a certain axial length of the elongate bore, the jacket surface of the coaxial cable has to be removed and the remaining coaxial cable comprising the outer conductor, the dielectric and the inner conductor is continued in the axial direction within the elongate bore. The outer conductor of the coaxial cable subsequently also has to be removed and the remaining components of the coaxial cable (dielectric and inner conductor) are fed further through in the axial direction in the elongate bore. From this section onward, a component of the high-pressure feedthrough takes over the function of the outer conductor. The dielectric of the coaxial cable is now also removed in a region axially offset therefrom and its function is taken over by a further component of the high-pressure feedthrough. Only the inner conductor of the coaxial cable now projects outward at the opening of the elongate bore disposed at the high-pressure side. The individual cable components accordingly have to be successively removed from the outside to the inside until only the uninsulated inner conductor remains and can exit the high-pressure feedthrough at the high-pressure side.
The function of the outer conductor can, for example, be taken over by the support structure of the high-pressure feedthrough. It may be designed as electrically conductive for this role. In addition, an electric contact of the support structure to the outer conductor of the coaxial cable may be necessary. This electrical connection may take place either by a direct contact or an alternative such as a curved metallic contact element.
An element of the high-pressure feedthrough taking over the function of the dielectric of the coaxial cable may be a sealing compound or a sealing element that is introduced into the elongate bore. This sealing compound or the sealing element also serves as the dielectric in addition to the sealing function of the high-pressure side with respect to the low-pressure side. For this purpose, it coaxially surrounds the inner conductor fed through the elongate bore in at least one part section of the elongate bore. A polymer compound, such as an epoxy resin, has proven to be a particularly suitable sealing compound that may be poured into the elongate bore and consequently enters into a connection having material continuity with the respective section of the support structure and the inner conductor.
The sealing element may be a special sealing body that is positioned at a corresponding point in the elongate bore. The sealing element is resilient and may compress. The sealing element may develop its full sealing effect on a corresponding pressure exertion from the high-pressure side.
In one embodiment, the elongate bore may have a plurality of sections having mutually differing diameters. Different components of the coaxial cable may be introduced in the different sections. Different functions of the coaxial cable may also be implemented by components of the high-pressure feedthrough. A first section of the elongate bore is, for example, in the region close to low pressure wherein the diameter is coordinated with the diameter of a conventional coaxial cable having a complete structure. A coaxial cable, including its jacket surface, may thereby be introduced into said section of the elongate bore with proper fit. Another embodiment may feature a bore diameter that is larger in this region and the cable can be introduced into the elongate bore with a sleeve surrounding the jacket.
In an embodiment an one adjoining further section is characterized by an inner diameter of the elongate bore reduced with respect to the first section. This reduced diameter allows a fitting reception of a coaxial cable in which at least one cable component has previously been removed. Different regions may be configured for proper fitting reception of a coaxial cable having a removed jacket or a removed jacket and outer conductor. These regions are may follow one another in the axial direction toward the high-pressure side.
Another embodiment may feature a further section having an increased inner diameter of the elongate bore. Only an inner conductor of the coaxial cable may be able to be introduced in this section. This section may be the region of the opening of the elongate bore toward the high-pressure side. An annular space may form due to the spacing of the inner wall from the inner conductor and said annular space may fill with fluid due to its opening toward the high-pressure side. The fluid inflowing in this region consequently lies around an introduced inner conductor in an annular and coaxial manner and may perform the function of the dielectric. The fluid may flow to the sealing compound introduced within the elongate bore or to the sealing element introduced within the elongate bore.
In an embodiment this fluid may flow toward the seal if the introduced sealing compound or the introduced sealing element is adjacent to at least one abutment within the elongate bore in the axial direction. As previously explained, the inflowing fluid of the high-pressure side moves up to the sealing compound or up to the sealing element within the elongate bore. An axially directed force may act on the sealing compound or the sealing element and presses it onto the abutment due to the pressurized fluid. A compression of the sealing compound or of the sealing element consequently occurs, whereby its sealing effect is improved. At least one abutment may be formed by a step-like diameter tapering of the elongate bore. A support element may be used in the elongate bore that comprises a suitable abutment surface for the sealing compound or sealing element. The support element likewise comprises a central bore through which the inner conductor can extend. The support element may provide sections having different outer diameters so that the element may extend over a plurality of sections of the elongate bore. The front face of the support element facing the sealing element may comprise a planar surface to provide an abutment surface that is large and stable.
The support element may comprise a comparatively strong material such as ceramic, glass, plastic or another non-electrically conductive material or a combination of the aforesaid materials.
In accordance with an embodiment, at least one cap nut seated on the outer periphery of the support structure may be provided to install the high-pressure feedthrough at a structure separating the high-pressure zone and the low-pressure zone. The high-pressure feedthrough may be screwed in a separating structure by means of the cap nut.
In addition, one or more outer sealing elements may be provided to enable a sealing introduction of the high-pressure feedthrough into the supporting structure. One or more O rings seated on the outer periphery of the support structure may serve this purpose.
Additionally, the present disclosure likewise relates to a hydraulic or pneumatic system which has at least one structure separating a high-pressure zone and a low-pressure zone and into which at least one high-pressure feedthrough may be introduced. At least one coaxial cable may be led through this high-pressure feedthrough from the low-pressure side into the high-pressure side.
In one embodiment a piston-in-cylinder unit is provided. The high-pressure feedthrough serves the feeding through of a coaxial cable from the outside into the high-pressure zone disposed within the cylinder or the feeding through the cylinder jacket or a corresponding housing part. The introduction of a coaxial cable into the cylinder space may be used in applications in which physical properties of the piston-in-cylinder unit should be detected by means of a measurement device. The current piston position may be determined using these measured parameters. The measurement process makes use of high-frequency signals that have to be coupled into or decoupled from the cylinder space by one or more coaxial cables.
One embodiment features a diameter of the section of the elongate bore forming the annular space and/or the diameter of the section of the elongate bore receiving the sealing compound or the sealing element may be coordinated with the dielectric properties of the fluid to be used so that both the fluid and the sealing compound or sealing element have similar dielectric properties to the original dielectric of the coaxial cable. Impedance deviations of the coaxial cable occur within the high-pressure feedthrough may thereby be achieved.
The LiView measurement process that is based on a vector measurement of the scatter parameters of a cylinder may be implemented by the measurement apparatus. Measurement frequencies on the order of 10 GHz may be used here. To couple and decouple these high-frequency signals into and out of the cylinder, the special high-pressure feedthrough is used whose very compact construction shape ensures the coaxial feedthrough of a high-frequency signal in the above frequency range to the high-pressure cylinder space.
Further advantages and properties of the disclosure will be explained in more detail in the following with reference to an embodiment shown in the figures.